Automated optical inspection and sorting systems have been used to inspect and sort various target specimens including fruits and vegetables, processed meat, baked goods, and other foodstuffs; to remove different types of recyclable material; and to sort foreign or defective items from supplies of wood chips. These systems typically employ video systems with charge-coupled device line scan cameras to acquire images of target specimens moved on a conveyor belt across an optical scanning area. Illumination of the specimens is generally provided by either broad-spectrum tubular fluorescent lamps or rare gas discharge lamps. Signal processing circuitry identifies variations in the shade of target specimen images and sorts target specimens accordingly.
Shipments of potato pieces, such as raw french fries, from producers often include defective pieces that may contain potato rot, potato eyes, or potato dark green flesh. It is desirable to remove such contaminants before shipping potato pieces to consumers or fast food outlets. The removal of defective pieces also helps to establish the actual quantity of acceptable pieces in a shipment.
Traditionally, consumers have preferred that potato pieces, such as french fries, be prepared from potatoes that had been peeled prior to being cut into pieces. Because of this preference, potato piece sorting systems built in the past have generally been configured to reject potato pieces bearing potato peel.
More recently, however, potato piece foods that are still peel bearing have surged in popularity. For example, peel-bearing french fries have become steadily more available and more accepted over the past several years. It is possible that consumers perceive these products to be more healthful and "natural" than their naked brethren.
Unfortunately, existing potato piece sorting systems are not very useful for removing peel-bearing defective potato pieces from a random mixture of defective and acceptable peel-bearing pieces because, as noted, such systems are configured to reject all peel-bearing pieces. Moreover, this inadequacy is not overcome by means of simple recalibration because current systems use broad band visible light, which makes it difficult to distinguish an otherwise acceptable peel-bearing potato piece region from a potato piece region that suffers from "potato eye, " is blighted by potato rot, or is dark green. Moreover, because potato peel is substantially opaque to visible spectrum light, a covering of peel inhibits defect inspection of a portion of the potato flesh.